Communication system networks are known to comprise a plurality of communication systems and a central controller. Each of the communication systems comprises a plurality of communication units, a limited number of communication resources that are transceived via a limited number of repeaters, and a communication resource allocator that allocates the communication resources among the plurality of communication units. The communication units, which may be mobile radios, portable radios, and/or portable radio/telephones, are typically arranged into communication groups and are generally located throughout the communication system network. Of the communication resources, which may be TDM slot locations, frequency carriers, pairs of frequency carriers, or any other RF transmission means, one is selected to function as a control channel. The control channel transceives operational information between the communication units and the central controller via the communication resource allocators.
As is known, a communication unit may establish a communication with other communication units within the communication system network by transmitting an inbound signalling word (ISW) to the central controller via the communication resource allocator of the communication system that the communication unit is located in. Upon receiving the request, the central controller processes it and, if the request is valid, the central controller allocates a communication resource in each of the communication systems that have a communication unit of the targeted talk group in it. The communication systems, which may also be communication sites, are coupled to and controlled by the central controller. If a communication system, or site, loses contact with the central controller, the communication system, or site, operates as an independent communication system but only for communication units that are located within its coverage area.
As is also known, when a communication is requested by a communication unit for its particular communication group (first communication group), the communication unit transmits an ISW requesting allocation of a communication resource for that group. Upon receipt of the requesting ISW, the central controller determines whether a communication resource is available in all the communication systems, or sites, for the first communication group. In more advanced communication systems networks, the central controller determines which communication systems have a communication unit of the first communication group registered in it and whether these communication systems have an available communication resource. In either network, the central controller will not place the call until all communication systems, or sites, have an available resource. Thus, the requesting call waits in a queue until all the communication systems have a resource available.
When the above mentioned call, the first call, is waiting for communication resources to become available, subsequent requests for communications may be received. If the subsequent request is for a second communication group and the second call does not overlap the first call, i.e. the second call will be placed in entirely different communication systems than the first call, the second call can be processed. However, if the second call has one communication system that overlaps the first call, the second call is placed in the queue and will not be placed until after the first call is processed. The second call is placed in the queue even if all of the communication systems that the second call will be placed in have an available communication resource. Therefore, a need exists for a method that will allow the central controller to efficiently process subsequently receive communication requests when other communication requests are pending.